Source: Hypertension image, Creative Commons: http://en.wikipedia.org/wiki/File:Grade_1_hypertension.jpg
The pressure that blood exerts on the wall of a vessel that is measured in units of millimeters of mercury (mmHg). Blood pressure is the driving force that creates blood flow throughout the vessels of the body.
One of the two measures of blood pressure, diastolic pressure is a lower pressure that occurs when the left ventricle of the heart is in diastole (resting) which causes the pressure in the systemic arteries to drop.
The clinical term for high blood pressure, a person is considered to be hypertensive after three consecutive measurements of 140/90 mmHg or higher.
One of two measures of blood pressure, systolic pressure is a higher pressure that occurs when the left ventricle of the heart is in systole (contracting) and pumping blood into the arteries, causing their pressure to increase.
A term used to describe when the muscular walls of a vessel tense causing the diameter of the vessel to decrease. Vasoconstriction increases blood pressure and makes it more difficult for blood to flow through a vessel.
The term used to describe when the muscular walls of a vessel relax causing the diameter of the vessel to enlarge. Vasodilation decreases blood pressure and makes it easier for blood to flow through a vessel.